This invention relates to a centrifugal separator, also known in the art as a “centrifugal filter”, which is designed so that it will operate in a manner achieving a self-cleaning effect.
Centrifugal separators are well known for separating liquids of different densities or for separating particulate matter from liquids. The principle of operation of such a centrifugal separator is that a housing contains a rotor which is supported therein to spin at high speed about a substantially vertical axis. Liquid from which contaminants are to be removed is supplied to the rotor at elevated pressure along the axis of rotation. As this liquid passes through the rotor, denser contaminant materials or particles are separated therefrom centrifugally and retained in the rotor, typically as a cake adhering to the interior surface of the rotor, which is cleaned or replaced at intervals.
Self-powered centrifugal separators in which the liquid from which contaminants are to be removed also provides the drive for the rotor have long been used in lubrication systems of vehicles, as well as in other industrial separation processes. GB 2160796 and GB 2296942 disclose self-powered centrifugal separators of the type which comprises a base, a substantially vertical spindle upstanding from the base, a rotor mounted on the spindle for rotation thereabout by reaction to liquid emission from rotor nozzles, the base having an inlet passage for said liquid and the spindle having an axial bore and outlets therefrom to supply liquid to the rotor from said inlet passage, and a cover mounted on the base and enclosing the rotor. In this type of separator the liquid is supplied at pressure from the base of the housing and flows upwards through the axial bore to outlets near the top of the bore, which is typically a blind bore. A releasable cap is typically mounted at the top of the spindle to secure the cover.
In its earlier GB2478578 A, the applicant disclosed a centrifugal separator, whether of the self-powered type or when powered independently of the liquid being filtered, specifically designed to enable abrasive contaminant particles to be separated and removed from a liquid. Such abrasive contaminant particles need to be removed from liquid in a variety of industrial processes, including from honing oil, grinding machine coolant, electrode discharge machining fluid, or oil quench fluid from furnaces, and in water purification processes. In a more specific example a centrifugal separator may be used to remove particulate matter from cooling liquids used in industrial cutting processes. Waste materials generated in the cutting process mix with the cooling liquid and must be removed if the liquid is to be recycled. Failure to remove accumulating waste material will reduce the effectiveness of the cooling liquid and could result in overheating of cutting process components.
In order to prevent abrasive particles contacting the rotor bearings and causing rapid wear of the bearings, sometimes after as little as 30 seconds operation, and in order to separate contaminant particles from a liquid which is not itself a lubricant, the rotor and the spindle are connected so as to rotate in unison and bearings for rotation of the spindle relative to the base are provided in a bearing housing fixed to the base so that the bearings are isolated from the rotor chamber through which the liquid passes and on the inner surface of which the contaminant particles are retained. An axial sealing arrangement, separate from the rotational bearings, and between the spindle and the base is also disclosed in GB 2478578 A.
All of the foregoing centrifugal separators are designed for continuous operation, i.e. continuous through flow of liquid from which contaminant particles are to be removed. In the case of self-driven centrifugal separators in vehicle lubrication systems the cake of contaminant particles formed on the interior surface of the rotor is typically cleaned out manually during annual or half yearly servicing. Single use, removable and discardable rotor linings have been proposed and used for this purpose in some circumstances to save on the labour time and general messiness of this cleaning operation.
In some situations in vehicle or other industrial engines, rotors of centrifugal separators may need to be cleaned out every month, or two or more times a month for maintaining effective trouble-free operation. However, in other situations where centrifugal separators are used, such as for separation of abrasive particles from cooling liquid in metal cutting operations, sludge-like deposits of contaminant may build up so quickly in the rotor that cleaning out every day or even several times a day is necessary or desirable. Not only is this time consuming, but the speed and efficiency of the dismantling and re-assembly operations depend on the skill of the operating personnel. As the balance of the rotor must be accurately re-established at each re-assembly, this may not be efficiently and effectively achieved, nor in a predictable time scale.
An object of the invention is at least to reduce the frequency of cleaning out of the interior of the rotor of a continuously operating centrifugal filter, in situations where quick or heavy build-up of contaminant debris occurs. A further object is to reduce to a minimum the requirement for cleaning out the rotor of a centrifugal separator which operates in a liquid line of continuous process activity.